The term unsaturated fatty acid ester oil is used herein to relate to acyl glycerides and phospholipids, i.e. compounds comprising an unsaturated fatty acid side chain linked by an ester group to an “alcohol” (e.g. polyol) residue. Such compounds are important dietary sources of fatty acids, in particular polyunsaturated fatty acids (PUFAs) and more especially the essential fatty acids. They may also serve as sources for dietary replacements of essential fatty acids, e.g. of conjugated linoleic acid (CLA) which may be used in a weight reduction diet. Particularly important essential fatty acids include the ω-3, ω-6 and ω-9 acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Other fatty acids commonly used in nutraceuticals and pharmaceuticals include arachidonic acid (AA), alpha linolenic acid (ALA), conjugated linolenic acid (CLN), dihomo-gamma linolenic acid (DGLA) and gamma linolenic acid (GLA). Such fatty acids typically will contain 12 to 26 carbons, more typically 16 to 22 carbons, and will have a saturated or mono- or poly-ethylenically-unsaturated hydrocarbyl chain.
Typical dietary sources of such fatty acid ester oils include lipids such as animal, fish, plant or microorganism triglycerides and phospholipids, especially the triglycerides. Mono or diglycerides however can equally be used as can other esters, e.g. lower alkyl (e.g. C1-6 alkyl, for example ethyl) esters as well as free fatty acids or physiologically acceptable salts thereof and fatty acid ester waxes. Particularly important sources are fish oils, in particular oily fish oils such as cod-liver oil, halibut-liver oil, etc. as these are rich in ω-3, ω-6 and ω-9 fatty acids.
However, as anyone who, in childhood, has been on the receiving end of fish oils will recall, the taste, mouthfeel and smell can be vile. In part this is due to the sensitivity to oxidation of the fish oil. As a result fatty acid ester oils tend to be administered in capsule form, containing liquid oil within a soft gel casing. Such capsule casings are usually made from mammalian gelatin, typically of porcine or bovine origin. In order to deliver a reasonable dose of the oil, the capsules tend to be rather large, sufficiently large indeed to cause problems swallowing them for the young and the elderly. As a result, ingestion often involves the capsule being chewed and bursting in the mouth releasing the unpleasantly tasting oil contents.
There is thus a continuing need for improved oral administration forms for unsaturated fatty acid ester oils.